In one embodiment of the present invention, an object of the invention is to provide a wireless communication-improving sheet member capable of increasing a possible communication distance of an IC tag for wireless communication, a wireless IC tag, an antenna, and a wireless communication system. A first spacer includes an arrangement face on which on which the wireless IC tag is disposed without a wired connection, and an auxiliary antenna is disposed on the first spacer on an opposite side to the arrangement face, the auxiliary antenna resonating with electromagnetic waves used in the wireless communication. The auxiliary antenna includes a first conductor layer as a resonant layer and a second spacer. The second spacer is disposed on an opposite side to the first spacer with the first conductor layer interposed therebetween. A discontinuous area is disposed in the first conductor layer of the auxiliary antenna. Thus, it is possible to not only eliminate influence of a communication-jamming member, but also increase received electrical power of a wireless IC tag (antenna), and ensure a long communication distance.